Neutron Oscillations Research Articles

Nuclear structure near the drip line studied by RNB

The use of radioactive nuclear beams (RNB) has provided an opportunity to study nuclei far from the stability line. Reaction studies using intermediate and high-energy (30–1000 AMeV) radioactive beams have revealed new structures of nuclei that are not seen in nuclei near to the stability line [1]. One such new structure is the neutron halo, a long low-density tail of the neutron distribution [2]. It has been observed in neutron drip-line nuclei, such as6He,11Li and11Be. The neutron halo has put light on many new structure problems. Among those, recent studies of a softE1 mode, a low-frequency oscillation of halo neutrons against the core, are discussed in the following section in connection with a recent (p, p′) reaction measurement [3]. Also, the effect of changes in single-particle orbitals on halo formation is discussed [4].

Bounds on ΔB = 1 couplings in the supersymmetric standard model

The most general supersymmetric model contains baryon number violating terms of the form λ ijk , D i D j U k in the superpotential. We reconsider the bounds on these couplings, assuming that lepton number conservation ensures proton stability. These operators can mediate n - n oscillations and double nucleon decay. We show that neutron oscillations do not, as previously claimed, constrain the λ dsu coupling; they do provide a bound on the λ dbu coupling, which we calculate. We find that the best bound on λ dsu arises from double nucleon decay into two kaons; the calculation is discussed in detail. There are no published limits on this process; experimenters are urged to examine this nuclear decay mode. Finally, the other couplings can be bounded by the requirement of perturbative unification.

Neutrino oscillations in matter

Neutron oscillations can be drammatically altered in the presence of matter. This effect can give a natural explanation of the solar neutrino problem. Recent experiments are analyzed in this framework and bounds on neutrino masses and mixing parameters are given.

The influence of magnetic fields on free neutron oscillations

The phenomenological two-state model usually used to describe the influence of external fields on neutron oscillations is illustrated and extended in order to take into account the vector character of magnetic fields. It is shown that, for sufficiently weak fields, the solution of the extended model can be reduced to the solution of three independent two-state models, one for each vector component. This result is useful for the calculation of antineutron losses in neutron oscillation experiments.

Neutron-antineutron oscillation of ultracold neutrons in storage vessels

If neutron-antineutron oscillations exist in nature, UC neutrons, confined in a storage box, may develop a tiny component of antineutrons that eventually annihilate inside the confining walls. The annihilation rate for this process is evaluated taking into account the effect due to the Earth's gravitational field. The result is employed to discuss how UC neutron experiments would compare with experiments with neutron beams.

Free neutron oscillations

The status of the free neutron oscillation search is described and the new experiment at the ILL reactor in Grenoble aiming at investigating the neutron-antineutron oscillation time up to 10 8 s is discussed.

"Gravitational" contributions to n-n-bar oscillations in vacuum.

The possibility that laboratory tests on neutron oscillations in a vacuum may be significantly affected by the local contribution of a possible vector-field component of the total effective gravitational interaction is not completely ruled out by present experimental data. It is suggested that performing various measurements with different flight times of the neutrons could make it possible to extract significant information on the existence of a vector partner of the graviton, and on its coupling to the baryon number.

The role of antiprotons in cosmic-ray physics

Though success eluded experimentalists from detecting cosmic-ray antiprotons over a long period of time, the study of cosmic-ray antiprotons has now become a fascinating field of research. In this review, we have attempted to elucidate the excitement in this area of research since the discovery of antiprotons in the laboratory. We have described the experiments carried out so far to measure the energy spectrum of antiprotons, from about 200 MeV to about 15 GeV, and summarised the results. The observed spectrum, with the limited data, appears to be very hard and is different from other components of cosmic radiation. Upper limits to the fraction of antiprotons in cosmic-rays have also been derived at higher energies, using the observed spectra of cosmic-ray primary and secondary particles at different depths in the atmosphere. We have described various physical processes by which antiprotons could be produced, such as high-energy interactions, neutron oscillations, evaporation of Mini Black Holes, decay of super symmetric particles, etc. The energy spectrum of antiprotons, which are produced through the above processes, undergoes modifications during propagation in the Galaxy. We have examined in detail the propagation models which have been employed to explain the observed data. It is shown that no single model could predict correctly the observed energy spectrum of antiprotons over the entire energy region. However, many models are able to explain the data at relativistic energies. It is difficult at this stage to make a choice among these models. The implications of these models for other components of cosmic-rays, such as positrons, deuterium, and He, have been discussed. We have examined the production of gamma rays in the Galaxy from sources, which produce the observed antiprotons through high-energy interactions. We have also briefly indicated the effect of possible re-acceleration during their confinement in the Galaxy. We finally emphasized the need for more detailed measurements of the spectral shape of cosmic-ray antiprotons to further refine speculations of their origin. Similarly, we have shown that detailed observation of the energy spectra of positrons, deuterium, and He at relativistic energies are crucial to test various propagation models.

Dressed neutrons.

When neutrons are exposed to a large number of electromagnetic quanta of arbitrary frequency their spin rotation about a static magnetic field can be suppressed completely. Further, natural-linewidth level-crossing signals in the neutron polarization can be produced. These observed effects are interesting also in connection with neutron electric-dipole-moment and neutron oscillation experiments. They are described in the dressed-particle formalism developed in atomic physics. We were able to reconstruct the dressed-neutron energy-level diagram experimentally.

Magnetic shielding of a large volume for an experiment on quasi free neutron oscillation

Results of the shielding against the Earth's magnetic field on a large volume are given. The experimental procedure is based on a multilayer μ-metal shield and a series of correcting electric coils. A final average value of (8.1±4.4) mG is obtained in a volume of about 20 m 3.

On the experimental possibilities of detecting multiple neutrons in massive samples

There are two types of rare nuclear transformations occurring in nature, which are accompanied by multiple neutron emission: spontaneous fission of uranium nuclei and hypothetical super-heavy elements, and spontaneous nuclear decay induced by nucleon decay or ñN annihilation in the process of neutron oscillation. The design and characteristics of a detector for registration of multiple neutron events are discussed.

Assessment of the parameters of a setup for searches for nucleon decay and neutron oscillation by detecting multiple neutron events in massive samples

The parameters are assessed of a detector designed to record nucleon decay and/or the oscillations of a neutron bound in the atomic nucleus by detecting multiple neutron emission events in massive samples. Calculations have been carried out for the detection efficiency and for the spatial distribution of the points at which the single neutrons emitted from a point source had to be detected, for different variants of the detector geometry. To evaluate the background characteristics of the detector, calculations have been performed for the multiplicities and spatial distributions of the points of formation of secondary neutrons occurring in the interactions of 0.3–1 GeV nucleons with infinite lead units. It is shown that the comparison of the spatial distribution of the points of neutron detection for nucleon decay or the neutron oscillation phenomena and the background processes allows one to suppress the cosmic-ray background of the detector by a factor of more than 10.

Test of the quasifree condition in neutron oscillation experiments

In neutron-antineutron oscillation experiments the quasifree condition defines the tolerable size of the residual magnetic field along the neutron beam. The best way to ensure that the quasifree condition is met during a neutron oscillation search is to use neutrons themselves for the measurement of the residual magnetic field, by observing neutron spin rotation along the neutron path of flight. We have tested such a neutron spin magnetometer, using a polarized neutron beam. A combined active plus passive shielding setup was developed for the magnetic shielding of the neutron beam.

Formula omitted] mixing inside nuclei

In this paper we improve upon a previous analysis of the n n mixing in nuclei. Our aim is to provide an estimate, as reliable as possible, in the n n oscillation time τ n n exploiting the experimental data on nuclear stability. To this purpose we explore the validity of the closure approximation in calculating the nuclear lifetime T and discuss a refined theoretical approach. Furthermore, we test the sensitivity of T to the forces and densities of both matter and antimatter. Our results essentially agree with some of other estimates and yield values for τ n n within the reach of the experimental searches for free neutron oscillations.

Nonlinearity in Weak Magnetic Fields Induced by Neutron-Antineutron Oscillations in Neutron Interferometry and Spin Resonance

Neutron oscillations introduce nonlinear behavior in the magnetic field dependence of the neutron energy. In principle these minute effects are observable if regeneration problems can be overcome, but general statistical arguments render this approach noncompetitive with direct observation of the antineutron.

Searches for proton decay and superheavy Magnetic Monopoles

In conclusion, as of 1984 January, it may be stated that the existence of super-heavy monopoles and the phenomenon of nucleon decay, both of which are extremely important from the point of view of grand unification theories, are still very open questions. While there has been just one magnetic monopole candidate so far, there have been several as far as nucleon decay is concerned. The first candidates for nucleon decay came from the fine-grain calorimeters of KGF, and NUSEX; recently there have been candidates from the water Cerenkov experiments as well. The experimental situation regarding the other important phenomena of relevance to grand unification which we have not discussed in this article — like the finite mass of neutrinos, neutrino oscillations, and neutron oscillations — continues to be indefinite though many dedicated experiments are in progress.

How supersymmetry naturally suppresses Higgs-boson-mediated baryon-number violation in SU_{C}(4)×SU_{L}(2)×SU_{R}(2) and SO(10)

The supersymmetric versions of the left-right-symmetric ${\mathrm{SU}}_{C}(4)\ifmmode\times\else\texttimes\fi{}{\mathrm{SU}}_{L}(2)\ifmmode\times\else\texttimes\fi{}{\mathrm{SU}}_{R}(2)$ Pati-Salam theory and the grand unified SO(10) theory are studied. In the minimal versions of these models the requirement of soft or spontaneous breaking of supersymmetry, together with renormalizibility, leads to an accidental global U(1) symmetry which leads to baryon-number conservation. A necessary condition for this symmetry to be broken is the existence of fields which are antisymmetric in at least two ${\mathrm{SU}}_{C}(4)$ indices. The introduction of such fields may allow for observable neutron oscillation.

Theory of neutron-antineutron oscillation using bottled ultracold neutrons

We contrast the quantum-mechanical treatment of neutron oscillations in a "bottle" with the usual free-space formalism. The quantum-mechanical corrections appear to reduce the figure of merit for the bottled-neutron experiments, and also place constraints on the experimental arrangement.

Study of the 25 K NpO2 Phase Transition by a Neutron Oscillation Camera

Study of the 25 K NpO2 Phase Transition by a Neutron Oscillation Camera

Neutron oscillations in a periodically varying magnetic field

We transform the driven-neutron-oscillation problem into a form similar to a magnetic-resonance problem in an internal space, and obtain an approximate analytical solution in the neighborhood of the resonances. The results are in good agreement with the numerical work of Arndt, Prasad and Riazuddin. We find that the n probability is quite insensitive to variations in magnetic-field strength and driving frequency when near a resonance maximum, the only critical aspect being the alignment between the static and oscillating fields.